Hitherto, various kinds of submerged type pumps are known as a pump used to exhaust liquefied gas contained in the storage tank. An example of the known pumps is explained by an overall concept diagram as shown in FIG. 3. First of all, to suck up a combustible liquefied gas from the storage tank 10, a fluid lifting column (hereinafter merely referred to as the column) 12 is vertically drawn down from the top of the storage tank 10 into the storage tank fluid and, furthermore, a submerged type pump 14 is suspended by a wire 18 through a winch 16 and set on the bottom inside the column 12.
When the submerged type pump 14 immersed in the storage tank fluid is activated, the treating fluid is delivered in the direction shown by an arrow of the solid line illustrated in the explanatory drawing of the delivery fluid of the conventional submerged type pumps as shown in FIG. 4. Namely, the handling fluid sucked through a suction port 22 of a pump section 20 is discharged through a discharge port 24 arranged on the boundary outer periphery between a motor section 26 and the pump section 20 and delivered to an exterior of the storage tank 10 while the column 12 is filled with the liquid. Further, when an operation of the pump section 20 is stopped, the residual fluid in the top of the submerged type pump 14 in the column 12 flows back in the direction of an arrow of the dotted line through the discharge port 24 and in turn is exhausted through the pump suction port 22 of the pump for gradual dipping and the dipping of the fluid is ceased for stabilization when reached at the same level as the fluid level in the storage tank 10.
Meanwhile, for the purpose of repair, inspection and the like, the submerged type pump is lifted up by the winder 16 such as the winch, hoist and the like through the wire 18 and after completion of repair or inspection, the pump is again descended to the bottom of the column for settlement of the seating face on the bottom of the column.
However, in case of restarting and operating such a pump as hereinbefore described, a desired discharge pressure may not be obtained before an inside of the column is filled with the fluid, and even a simple stop of the pump causes the fluid in the column to flow back to the storage tank resulting in drop of the fluid level so that the pump can not be started instantly, for which reason preparation of the fluid delivery by the pump requires much time with insufficient fluid delivery. Furthermore, in case a swing operation takes place by arranging a spare pump on one storage tank, it is still impossible to store the fluid in the column equipped with the spare pump, resulting in an intermittent operation of the pump with the problems of higher cost for fluid delivery and difficult operation.
Hence, the purpose of the invention is to provide a submerged type pump for liquefied gas, not only capable of preventing back-flow of the handling fluid remained on the top of the pump in the column but also capable of properly exhausting the fluid as desired allowing a consecutive operation with an efficient fluid delivery.
To accomplish the aforementioned purpose, there is provided a submerged type pump which is vertically seated on the seating face arranged on the bottom of the fluid lifting column and is comprised of a motor section and a pump section with a casing in which the handling fluid may pass, characterized in that a check valve is arranged at a pump discharged port and an automatic switch valve is arranged on the top of the casing so that the automatic switch valve is released by closing the fluid lifting column with the pump seating face and the check valve to discharce the handling fluid suspended in the fluid lifting column.
Further, in the submerged type pump according to the invention, the seat is tapered to which the pump is seated to close the fluid lifting column.